The stimulating effect of a cold, dark pretreatment on the etioplast/chloroplast transformation of angiosperms. I. The stimulating effect of cold predarkening on different stages of greening under white light

Schönbohm, E., Stute, U., Thienhaus, P. and Werner, U. 1988. The stimulating effect of a cold, dark pretreatment on the etioplast/chloroplast transformation of angiosperms I. The stimulating effect of cold predarkening on different stages of greening under white light. - Physiol. Plant. 72: 541–546.
The etioplast/chloroplast transformation in angiosperms is controlled by light; most of the processes are mediated by phytochrome. We have shown that in the primary leaves of etiolated seedlings of wheat ( Triticum aestivum L. cv. Kolibri), fire-bean ( Phaseolus multiflorus L. cv. Preisgewinner) and in the cotyledons of etiolated sun flower seedlings ( Helianthus annuus L. cv. macrocarpa) the chlorophyll accumulation in the phase after the end of the lag phase can be greatly stimulated by a cold predarkening period. This effect is not necessarily coupled with a red preirradiation. Furthermore the lag phase can be dramatically shortened by the cold, dark pretreatment, whereas the amount of photoconvertible protochlorophyll(ide) in the darkness remains unaffected by the cold, dark pretreatment. The stimulating effect of a cold, predarkening period on greening is fully reversible by a warm, dark phase that is placed between the cold period and the onset of the continuous white light phase. These findings cannot be generalized: We could demonstrate that in the tropical plant Momordica charantia greening under white light was not affected by different temperature pretreatments during predarkening. The stimulating effect of a cold, predarkening period on greening is assumed to have ecological relevance.     

Localization of immunoreactive epidermal growth factor receptors in human nervous system

Epidermal growth factor is a well-defined peptide which stimulates cell growth and elicits cell responses in a variety of tissues by binding to specific receptors, EGF-R. A specific antiserum against the EGF receptor, which has previously been used to characterize EGF-R in human skin, fibroblasts, and smooth muscle, was used to survey the distribution of EGF-R in human nervous system. Portions of formalin-fixed, paraffin-embedded autopsy specimens were examined by use of immunohistochemical staining (PAP technique) with EGF-R antiserum. Many types of nerve cells, e.g., cerebral cortical pyramidal cells, hippocampal pyramidal cells, Purkinje cells, anterior horn cells, and dorsal root ganglion neurons, contained immunoreactive EGF-R. However, immunoreactive EGF-R were not detected in astrocytes, oligodendrogliocytes, and other small neurons such as granule cells. Intense immunostaining for EGF-R was also detected in ependymal cells from choroidal and extrachoroidal locations. Although immunoreactive EGF-R is widely distributed in human nervous system, the functional role of EGF and its receptor in the nervous system remains unknown.     

Ventilation inhomogeneity during controlled ventilation. Which index should be used?

Six indexes for diagnosing uneven ventilation by tracer gas washout were studied. The indexes were lung clearance index, mixing ratio, Becklake index, multiple-breath alveolar mixing inefficiency, moment ratio, and pulmonary clearance delay, all of which increase with impaired pulmonary gas mixing. In model lung tests, indexes that compared the actual washout curve with a calculated ideal curve (mixing ratio, multiple-breath alveolar mixing inefficiency, and pulmonary clearance delay) were unaffected by changes in tidal volume and series dead space, whereas the others varied markedly. In both spontaneously breathing and mechanically ventilated patients all indexes showed a significant difference between smokers and nonsmokers (P less than 0.002), but the indexes were somewhat different in their assessment of different ventilatory patterns. However, the mean value for all indexes, with the exception of mixing ratio, was smallest with a fast insufflation followed by an end-inspiratory pause. Any of the indexes may be useful if its limitations are recognized, but mixing ratio, multiple-breath alveolar mixing inefficiency, and pulmonary clearance delay seem preferable, because they are not affected by changes in tidal volume and dead space fraction.     

Effect of mutations in a zinc-binding domain of yeast RNA polymerase C (III) on enzyme function and subunit association.

The conserved amino-terminal region of the largest subunit of yeast RNA polymerase C is capable of binding zinc ions in vitro. By oligonucleotide-directed mutagenesis, we show that the putative zinc-binding motif CX2CX6-12CXGHXGX24-37CX2C, present in the largest subunit of all eukaryotic and archaebacterial RNA polymerases, is essential for the function of RNA polymerase C. All mutations in the invariant cysteine and histidine residues conferred a lethal phenotype. We also obtained two conditional thermosensitive mutants affecting this region. One of these produced a form of RNA polymerase C which was thermosensitive and unstable in vitro. This instability was correlated with the loss of three of the subunits which are specific to RNA polymerase C: C82, C34, and C31.     

Generating compatible translation initiation regions for heterologous gene expression in Escherichia coli by exhaustive periShine-Dalgarno mutagenesis. Human glutathione reductase cDNA as a model.

Adaptation of eucaryotic cDNA to heterologous expression was studied by mutating the translation initiation (TI) region upstream (mTI) and downstream (MTI) of the start codon. In the mTI subregion the 8 bases flanking the invariant Shine-Dalgarno motif GG-AG were mutagenized exhaustively, while the MTI subregion was subjected to random silent mutations at the wobble positions. The quality of a given TI sequence was judged on the basis of expressed enzyme activity. Low-yield and high-yield mutants of both TI subregions were selected and recombined systematically. The analysis of these double cartridges gave the following results: 1. As a rule, an unfavourable MTI subregion can be compensated for by mutations in the mTI subregion and vice versa. 2. The compatibility between mTI and MTI subregion is explainable at least in part by a low interaction tendency; a delta G(o)'-value of -10.7 kcal/mol appears to be a physical threshold for heterologous cDNA expression. 3. On the basis of periShine-Dalgarno mutations, the expression yield for different cDNA sequences could be increased by 1 to 2 orders of magnitude. One of these sequences encoded delta(1-15)human glutathione reductase, a mutant lacking the flexible N-terminal extension of the protein. In conclusion, to study and overcome TI region-based expression problems it is worthwhile to start out with a versatile vector containing exhaustive mutations in the periShine-Dalgarno sequences; as a rule the coding MTI subregion can be kept unchanged.     

Calcium is necessary for light excitation in barnacle photoreceptors

Summary Illumination of barnacle (Balanus amphitrite) photoreceptors is known to increase the membrane permeability to sodium and Ca²⁺ ions resulting in a depolarizing receptor potential. In this report, we show that lanthanum (La³⁺), a known inhibitor of Ca-binding proteins, reversibly eliminates the receptor potential of barnacle photoreceptors when applied to the extracellular space. Similar reversible elimination of the light response was obtained by removing extracellular Ca²⁺ by application of the calcium chelating agent EGTA. Iontophoretic injection of Ca²⁺, but not K⁺ into the cells protected both the transient and the steady-state phases of the receptor potential from elimination by EGTA while only the transient phase was protected in the presence of La³⁺. The EGTA experiments suggest that internal Ca²⁺ is necessary for light excitation of barnacle photoreceptors while the La³⁺ experiments suggest that La³⁺-sensitive inward current is necessary to maintain excitation during prolonged light.Abbreviations EGTA ethylenglyol-bis-(-aminoethylether) N, N, N¹, N¹-tetraacetate - BAPTA bis-(0-aminophenoxy)-ethane-N, N, N¹, N¹-tetraacetic acid - DMSO dimethyl sulfoxide - trp transient receptor potential - nss no steady state - ASW artificial sea water     

haemolysin of Escherichia coli: Comparison of pore-forming properties between chromosome and plasmid-encoded haemolysins

Abstract Lipid bilayer experiments were performed with chromosome-encoded haemolysin of Escherichia coli . The addition of the toxin to the aqueous phase bathing lipid bilayer membranes of asolectin resulted in the formation of transient ion-permeable channels with two states at small transmembrane voltages. One is prestate (single-channel conductance 40 pS in 0.15 M KCl) of the open state, which had a single-channel conductance of 420 pS in 0.15 M KCl and a mean lifetime of 30 s. Membranes formed of pure lipids were rather inactive targets for this haemolysin. Experiments with different salts suggested that the haemolysin channel was highly cation-selective at neutral pH. The mobility sequence of the cations in the channel was similar if not identical to their mobility sequence in the aqueous phase. The single-channel data were consistent with a wide, water-filled channel with an estimated minimal diameter of about 1 nm. The pore-forming properties of chromosome-encoded haemolysin were compared with those of plasmid-encoded haemolysin. Both toxins share common features, oligomerize probably to form pores in lipid bilayer membranes. Both types of haemolysin channels have similar properties but different lifetimes.